Exhaust emission control device

ABSTRACT

An exhaust emission control device includes a reducing agent adding valve for injecting a reducing agent into an exhaust pipe. The adding valve has a tip end portion having a nozzle and facing an internal space of the exhaust pipe. The tip end portion is disposed outwardly of an inner circumferential surface of the exhaust pipe. The adding valve is kept out of direct striking contact with the exhaust gas and hence is substantially free from thermal degradation and adhesion of deposits.

CROSS REFERENCE TO RELATED APPLICATION

The present application is based on and claims priority from Japanese Patent Application No. 2007-112153, filed Apr. 20, 2007, the content of which is incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an exhaust emission control device for purifying engine exhaust gas by reduction with a reducing agent.

2. Description of the Related Art

Exhaust emission control devices for purifying engine exhaust gas by way of reduction of nitrogen oxides (NOx) with a reducing agent are known heretofore. The reducing agent is urea water, for example, in which instance ammonia (NH₃) generated from urea by decomposition reacts with NOx in the presence of a catalyst to produce harmless nitrogen (N₂) and water (H₂O), thereby purifying the NOx.

One example of such known exhaust emission control devices is disclosed in Japanese Patent Laid-open Publication (JP-A) No. 2006-207395. The disclosed device includes an adding valve for injecting a reducing agent, and a collision scattering mechanism for scattering the injected reducing agent by collision of the reducing agent with the impact scattering mechanism. The adding valve is directly mounted to the tubular wall of an exhaust pipe. In the disclosed exhaust emission control device, the adding valve has a tip end portion projecting into the exhaust pipe, and the reducing agent is injected from a nozzle of the tip end portion directly into an internal space of the exhaust pipe. The injected reducing agent is then scattered by the collision scattering mechanism into exhaust gas, and finally introduced into a catalyst.

With this arrangement, however, since the tip end portion of the adding valve is subjected to high temperatures due to direct striking contact with the exhaust gas, there is a risk of the adding valve being thermal degraded or deposits adhering to the body of the adding valve.

SUMMARY OF THE INVENTION

With the foregoing problem in view, an object of the present invention is to provide an exhaust emission control device, which is capable of purifying engine exhaust gas by reduction with a reducing agent injected from a reducing agent adding valve while keeping the adding valve out of the direct striking contact with the exhaust gas.

To achieve the object, there is provided according to the present invention an exhaust emission control device comprising: an exhaust pipe for the passage therethrough of exhaust gas; and a reducing agent adding valve for injecting a reducing agent into the exhaust pipe, wherein the reducing agent adding valve has a tip end portion having a nozzle and facing an internal space of the exhaust pipe, the tip end portion being disposed outwardly of an inner circumferential surface of the exhaust pipe.

With this arrangement, since the tip end portion of the reducing agent adding valve faces the internal space of the exhaust pipe without projecting into the internal space of the exhaust pipe, the reducing agent adding pipe is able to inject the reducing agent into the internal space of the exhaust pipe while the tip end portion is kept out of direct striking contact with the exhaust gas.

Preferably, the exhaust emission control device further comprises a collision scattering mechanism disposed in the exhaust pipe at a position intersecting with an injecting direction of the reducing agent for collision with the injected reducing agent to scatter the reducing agent into the exhaust gas.

The collision scattering mechanism promotes atomization of the injected reducing agent, ensuring uniform and efficient scattering or dispersal of the reducing agent into the exhaust gas.

Preferably, the reducing agent adding valve is mounted to a mounting portion formed integrally with a tubular wall portion of the exhaust pipe.

With this arrangement, the reducing agent adding valve, the collision scattering mechanism and a part of the entire exhaust pipe can be assembled into a single module. This will provide an increased degree of freedom in arranging the reducing agent adding valve and the collision scattering mechanism.

Preferably, the reducing agent adding valve is disposed in such a manner as to inject the reducing agent in a direction perpendicular to an axial direction of the exhaust pipe, and the collision scattering mechanism is disposed directly beneath the nozzle of the reducing agent adding valve.

This arrangement ensures reliable collision of the injected reducing agent with the collision scattering mechanism and the resulting high scattering efficiency of the reducing agent.

Preferably, the collision scattering mechanism is configured to convert a stream of exhaust gas into a swirling flow of exhaust gas.

With this conversion into the swirling flow, dispersion or scattering of the reducing agent into the exhaust gas can be achieved with improved efficiency.

Preferably, the collision scattering mechanism includes a plurality of fan-shaped fins tilted in a downstream direction of the exhaust pipe and arranged successively in a circumferential direction of the exhaust pipe so as to convert the stream of exhaust gas into the swirling flow of exhaust gas.

It is preferable that the nozzle of the adding valve has a longitudinal axis offset from a longitudinal axis of the exhaust pipe. This arrangement ensures that the reducing agent injected from the nozzle is entrained in the swirling flow of exhaust gas and uniformly scattered or dispersed into the exhaust gas.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagrammatical view showing a general configuration of an exhaust emission control device according to the present invention;

FIG. 2A is a front elevational view of a module of the exhaust emission control device when viewed from an upstream side of the flow of exhaust gas; and

FIG. 2B is a right side view of FIG. 2A, showing an internal structure of the module.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

One preferred embodiment of an exhaust emission control device according to the present invention will be described below in greater detail with reference to FIGS. 1 and 2A-2B.

The exhaust emission control device 1 is constructed to supply by injection a reducing agent into engine exhaust gas to thereby depurate nitrogen oxides (NOx) contained in the exhaust gas through the reduction of the NOx with the reducing agent. The reducing agent is urea water, for example. In this case, ammonia (NH₃) generated from urea by decomposition reacts with NOx in the presence of a catalyst to produce harmless nitrogen (N₂) and water (H₂O), thereby depurating the NOx.

The exhaust emission control device 1 generally comprises an exhaust pipe 2 for the passage therethrough of the exhaust gas, a reducing agent adding valve (hereinafter referred to, for brevity, as “adding valve”) 3 for injecting the reducing agent into the exhaust pipe 2, a supply pump 5 for drawing the reducing agent from a predetermined tank 4 into itself and forcing the reducing agent therefrom to the adding valve 3, a collision scattering mechanism 6 for collision with the injected reducing agent to scatter the same into the exhaust gas, and an electronic control unit (ECU) 7 for controlling operation of the adding valve 3, pump 5 and so on.

The ECU 7 is a microcomputer known per se, which is composed of a central processing unit (CPU) having a controlling function and a calculating function, a storage device including a read-only memory (ROM) and a random access memory (RAM), an input device and an output device.

The exhaust pipe 2 forms a part of an exhaust gas flow passage disposed upstream of a catalyst. The exhaust pipe 2 includes a tubular wall portion 10 having a length of about 10 cm in an axial direction thereof, and a pair of flanges 11 at opposite ends of the tubular wall portion 10 for connection with another exhaust gas flow passage member. The adding valve 3 is mounted to the exhaust pipe 2 and the impact scattering mechanism 6 is disposed in the exhaust pipe 2, so that the exhaust pipe 2, adding valve 3 and impact scattering mechanism 6 are assembled into a single module that can be handled as a single functional unit.

The exhaust pipe 2 has a mounting portion 12 to which the adding valve 3 is mounted. The mounting portion 12 is in the shape of a tube formed integrally with the tubular wall portion 10 and projecting in a radial outward direction which is perpendicular to the axial direction of the exhaust pipe 2 and also upward in FIGS. 1 and 2A-2B. The tubular mounting portion 12 has an internal space connected to an internal space of the exhaust pipe 2. The adding valve 3 is mounted to the exhaust pipe 2 with its tip end portion 13 fitted in the mounting portion 12.

The adding valve 3 receives therein the reducing agent which has been discharged from the supply pump 5, guides the received reducing agent to the tip end portion 13, and finally injects the reducing agent from a nozzle 13 a (FIGS. 2A and 2B) opening at a front end face of the tip end portion 13. The adding valve 3 is mounted to the mounting portion 12 in such a manner as to inject the reducing agent in a direction perpendicular to the axial direction of the exhaust pipe 2. The tip end portion 13 of the adding valve 3 is received in the tubular mounting portion 12 such that the tip end portion 13 is disposed outwardly of an inner circumferential surface 10 a (FIGS. 2A and 2B) of the tubular wall portion 10 and faces the internal space of the exhaust pipe 2. That is, the front end face of the adding valve tip end portion 13 at which the nozzle 13 a opens is offset from the inner circumferential surface 10 a of the tubular wall portion 10 of the exhaust pipe 2.

The adding valve 3 comprises an electromagnetic solenoid valve having a valve element (not shown) disposed normally in a position to close the nozzle 13 a and adapted to be actuated to open the nozzle 13 by magnetic attracting force produced when a solenoid coil (not shown) is energized. That part of the reducing agent, which has not been injected from the adding valve 3, is returned to the tank 4.

As shown in FIG. 2B, the collision scattering mechanism 6 is disposed directly beneath the nozzle 13 a of the adding valve 3 at a position intersecting with an injecting direction of the reducing agent within the internal space of the exhaust pipe 2. As best shown in FIG. 2A, the collision scattering mechanism 6 is composed of a plurality (four in the illustrated embodiment) of sectored or fan-shaped fins 16, 17, 18, 19 having a central angle of 90° and substantially the same radius.

As shown in FIG. 2A, the four fins 16-19 are disposed in an upper left region, an upper right region, lower right region and lower left region, respectively, that are formed by dividing a circular cross-sectional area of the internal space of the exhaust pipe 2 into four equal parts. The upper left fin 16 and the lower right fin 18 are arranged to tilt at an appropriate angle (45°, for example) from a vertical plane toward a downstream direction about one side thereof extending in parallel to each other in a horizontal direction (left-and-right direction in FIG. 2A). Similarly, the upper right fin 17 and the lower left fin 19 are arranged to tilt at an appropriate angle (45°, for example) from the vertical plane toward the downstream direction about one side thereof extending in parallel to each other in a vertical direction (upward-and-downward direction in FIG. 2A). With the fins 16-19 thus arranged, a linear stream of exhaust gas flowing straight ahead in the axial direction of the exhaust pipe 2, as it passes through the collision scattering mechanism 6, is converted by the fins 16-19 into a swirling flow of exhaust gas running in a circumferential direction of the exhaust pipe 2.

As shown in FIG. 2A, the tubular mounting portion 12 has a longitudinal axis offset or displaced to the right from a longitudinal axis of the tubular wall portion 10 of the exhaust pipe 2, so that the injecting direction of the reducing agent from the nozzle 13 a intersects mainly with the lower right fin 18. The longitudinal axis of the mounting portion 13 also forms a longitudinal axis of the nozzle 13 a of the adding valve 3. Accordingly, the reducing agent injected from the nozzle 13 a in a vertical downward direction impinges on the lower right fin 18 where the injected reducing agent is deflected by the lower right fin 18 in an axial downstream direction of the exhaust pipe 2. In this instance, the reducing agent is entrained in the swirling flow of exhaust gas and subsequently guided into the catalyst while it is uniformly dispersed into the exhaust gas.

As thus far described, an exhaust emission control device 1 according to the preferred embodiment of the present invention comprises an exhaust pipe 2 for the passage therethrough of exhaust gas, and a reducing agent adding valve 3 for injecting a reducing agent into the exhaust pipe 2. The adding valve 3 has a tip end portion 13 having a nozzle 13 a and facing an internal space of the exhaust pipe 2. The tip end portion 13 is disposed outwardly to an inner circumferential surface 10 a of the exhaust pipe 2.

With this arrangement, since the tip end portion 13 of the adding valve 3 faces the internal space of the exhaust pipe 2 without projecting into the internal space of the exhaust pipe 2, the adding pipe is able to inject the reducing agent into the internal space of the exhaust pipe 2 while the tip end portion 13 is kept out of direct striking contact with the exhaust gas. Thus, the adding valve 3 is substantially free from thermal degradation or adhesion of deposits.

Furthermore, the exhaust emission control device 1 further comprises a collision scattering mechanism 6 disposed in the exhaust pipe 2 at a position intersecting with an injecting direction of the reducing agent for collision with the injected reducing agent to scatter the reducing agent into the exhaust gas. The thus provided collision scattering mechanism 6 promotes atomization of the injected reducing agent, ensuring uniform and efficient scattering or dispersal of the reducing agent into the exhaust gas.

The exhaust pipe 2 has a mounting portion 12 formed integrally with a tubular wall portion 10 of the exhaust pipe 2, and the adding valve 3 is mounted to the mounting portion 12. With this arrangement, the adding valve 3, the collision scattering mechanism 6 and the exhaust pipe 2 can be assembled into a single module. This will provide an increased degree of freedom in arranging the adding valve 3 and the collision scattering mechanism 6.

The adding valve 3 is disposed in such a manner as to inject the reducing agent in a direction perpendicular to an axial direction of the exhaust pipe 2, and the collision scattering mechanism 6 is disposed directly beneath the nozzle 13 a of the adding valve 3. This arrangement ensures reliable collision of the injected reducing agent with the collision scattering mechanism 6 and the resulting highly efficient scattering or dispersal of the reducing agent into the exhaust gas.

The collision scattering mechanism 6 is configured to convert a stream of exhaust gas into a swirling flow of exhaust gas. With this conversion into the swirling flow, dispersion of the reducing agent into the exhaust gas can be achieved with improved efficiency.

Although in the illustrated embodiment the exhaust emission control device 1 is provided with the collision scattering mechanism 6 for promoting atomization of the injected reducing agent, the collision scattering mechanism 6 may be omitted. The adding valve 3 in the illustrated embodiment is arranged to inject the reducing agent in a direction perpendicular to the axial direction of the exhaust pipe 2. The adding valve 3 may be arranged in such a manner as to inject the reducing agent in a direction inclined at an angle to the axial direction of the exhaust pipe 2.

Obviously, various minor changes and modifications are possible in the light of the above teaching. It is to be understood that within the scope of the appended claims the present invention may be practiced otherwise than as specifically described. 

1. An exhaust emission control device comprising: an exhaust pipe for the passage therethrough of exhaust gas; and a reducing agent adding valve for injecting a reducing agent into the exhaust pipe, wherein the reducing agent adding valve has a tip end portion having a nozzle and facing an internal space of the exhaust pipe, the tip end portion being disposed outwardly of an inner circumferential surface of the exhaust pipe.
 2. The exhaust emission control device according to claim 1, further comprising: a collision scattering mechanism disposed in the exhaust pipe at a position intersecting with an injecting direction of the reducing agent for collision with the injected reducing agent to scatter the reducing agent into the exhaust gas.
 3. The exhaust emission control device according to claim 2, wherein the exhaust pipe has a tubular wall portion and a mounting portion formed integrally with the tubular wall portion, the reducing agent adding valve being mounted to the mounting portion of the exhaust pipe.
 4. The exhaust emission control device according to claim 2, wherein the reducing agent adding valve is disposed in such a manner as to inject the reducing agent in a direction perpendicular to an axial direction of the exhaust pipe, and the collision scattering mechanism is disposed directly beneath the nozzle of the reducing agent adding valve.
 5. The exhaust emission control device according to claim 3, wherein the reducing agent adding valve is disposed in such a manner as to inject the reducing agent in a direction perpendicular to an axial direction of the exhaust pipe, and the collision scattering mechanism is disposed directly beneath the nozzle of the reducing agent adding valve.
 6. The exhaust emission control device according to claim 2, wherein the collision scattering mechanism is configured to convert a stream of exhaust gas flowing in the axial direction of the exhaust pipe into a swirling flow of exhaust gas running in a circumferential direction of the exhaust pipe.
 7. The exhaust emission control device according to claim 6, wherein the collision scattering mechanism includes a plurality of fan-shaped fins tilted in a downstream direction of the exhaust pipe and arranged successively in a circumferential direction of the exhaust pipe so as to convert the stream of exhaust gas into the swirling flow of exhaust gas.
 8. The exhaust emission control device according to claim 6, wherein the nozzle of the adding valve has a longitudinal axis offset from a longitudinal axis of the exhaust pipe.
 9. The exhaust emission control device according to claim 7, wherein the nozzle of the adding valve has a longitudinal axis offset from a longitudinal axis of the exhaust pipe. 